This invention relates to primer compositions which are homogeneous, fluid, uncured suspensions or discrete particles of a modified propylene polymer in a film forming resin and methods for making and using these primers.
Primer compositions are frequently used to bond a polypropylene layer to a variety of substrates, including various metals. These primers often contain particles of a modified propylene polymer in an organic liquid, such as kerosene or Isopar, and sometimes also include a film forming resin such as an epoxy resin. However, these primer compositions suffer from several drawbacks. For instance, those which do not contain the film forming resin may not form a uniform coating on the surface to be bonded, resulting in poor bonding. On the other hand, when the film forming resin is employed, it is often incompatible with the organic solvent which contains the modified propylene polymer making it difficult, if not impossible, to blend enough of the modified propylene polymer particles into the film forming resin to make a useful primer composition.
It has now been unexpectedly found that a primer composition consisting essentially of a homogeneous, fluid, uncured suspension of discrete particles of a polar group-containing modified propylene polymer in a film forming resin material, the particles having an average particle size of less than 5 microns, and the primer composition being substantially free of solvent for the polar group-containing modified propylene polymer eliminates the drawbacks encountered with currently used primers and provides superior bonding properties.